1. Field of the Invention
The invention generally relates to a flexible disk recording and/or reproducing apparatus. More particularly, the invention relates to an improved apparatus for accurately positioning a rotated flexible disk with respect to a recording and/or reproducing head to record or reproduce information on the disk.
2. Description of the Prior Art
For successfully recording or reproducing information on a magnetic disk, particularly at high densities such as employed in video or computer equipment, the head-to-disk relation should remain substantially constant over a wide range of operating parameters. Variations in the head-to-disk relation can have a significant effect on the fringing flux pattern and therefore on the resolution of the sensing and recording of information on the magnetic disk. Unfortunately, with a magnetic disk, especially one that is flexible, as for example a floppy disk, the head-to-disk relation may be varied by the interaction of many parameters, such as temperature, humidity, relative speed between the disk and the head, penetration of the head into the disk, the contour of surfaces in the vicinity of the head or the disk, flexibility and variations in the thickness of the disk, the angles of attack and tilt of the head with respect to the disk, etc.
Various recording and/or reproducing apparatus have been proposed which seek to ensure a substantially constant relation between a flexible magnetic disk and a magnetic head during rotation of the disk. For example, in U.S. Pat. No. 3,178,719, a flexible magnetic disk supported in close proximity to a flat air bearing surface of an annular plate, usually referred to as a Bernoulli plate, is rotated at a relatively high speed with respect to the plate. This causes the rotated flexible disk to assume a stable planar position at a small distance from the air bearing surface. It is believed that the stable position results from a balance of the centrifugal and Bernoulli forces. A plurality of magnetic heads radially disposed with respect to the rotated flexible disk are embedded in the Bernoulli plate. The heads are either slightly above, slightly below, or flush with the air bearing surface. Since the close spacing between the air bearing surface and the rotated disk, and therefore the critical spacing between the magnetic heads and the rotated disk, varies as a function of the disk radius, a vacuum source is included to create a partial vacuum in respective round openings in the plate which each contain one of the heads. The partial vacuum deforms small annular areas of the flexible disk around the magnetic heads to independently control the close spacing between each of the heads and localized portions of the disk. This, it is asserted, maintains the head-to-disk spacing substantially constant and provides a close magnetic coupling between each head and the disk.
Although the recording apparatus disclosed in U.S. Pat. No. 3,178,719 may perform satisfactorily, it requires the use of a vacuum source to control the critical head-to-disk spacing. This significantly increases the construction and operating costs of such apparatus. A somewhat simpler recording apparatus that can deform small areas of a flexible disk around a magnetic head without the use of a vacuum source is disclosed in U.S. Pat. No. 3,731,292. In that apparatus, a flexible disk is rotated at a sufficient speed to cause the disk to revolve essentially in a plane. A magnetic head is moved radially inward across the rotated disk to record information on the disk. A finger member has a channel which extends the full length of travel of the head. The finger member is positioned in the plane of the rotated disk to cause successive portions of the disk crossing the channel to be deflected from the plane. At the same time, the head is located part way in the channel to cause a deflected portion of the disk to be reverse deflected into the channel. Thus the reverse deflected portion of the disk is deformed about the head. This, it is asserted, provides an intimate head-to-disk interface which assures a close magnetic coupling between the head and the disk.
One problem with the recording apparatus disclosed in U.S. Pat. No. 3,731,292 arises from the fact that the channel in the finger member has a uniform width. As a result, a deflected portion of the rotated disk which is reverse deflected into the channel is prevented by the parallel sides of the channel from conforming with the radially directed forces along the rotated disk. This appears to create an instability of the rotated disk in the vicinity of the magnetic head which will vary the head-to-disk spacing as the magnetic head is moved radially inward across the disk, thereby significantly affecting the resolution of the sensing and recording of information on the disk.
Another problem with the recording apparatus disclosed in U.S. Pat. No. 3,731,292 is that the rotated disk will seek to flare or deform increasingly away from the finger member in a radially outward direction, beginning at the innermost portion of the disk in contact with the finger member. Consequently, the rotated disk will be less stable proximate its outer edge than at an inner portion of the disk, and the head-to-disk spacing will therefore vary as the head is moved radially inward across the disk.